Four groups of studies are proposed to examine the human infant's behavioral and physiological responses to stress. The focus of the work is on the pituitary-adreno-cortical system, a neuroendocrine system that plays a central role in stress-resistance. The goals of the research are 1) to characterize the infant's behavioral and adrenocortical responses to stimulation, particularly with role of novelty/uncertainty as primary psychological triggers of stress responses; 2) to examine infant and maternal characteristics that may influence that infant's psychobiological response to stressful events; 3) to begin to extend our analyses to consideration of Ill and Well premature infants who must cope with the stressors of illness and/or necessary NICU procedures; and 4) to develop paradigms to examine the relations between adrenocortical and a) brain evoked potentials b) activity of the immune system, and c) activity o the autonomic nervous system in human infants. Subjects will be male and female infants aged birth to 15 months. Ecologically relevant stressor will be examined in these studies, including: gavage feeding (premature infants), PKU blood-test, discharge exam, circumcision, (full-term newborns), inoculations, maternal separation, entering daycare, strangers, and novel experiences (infants 2 months and older). Activity of the adrenocortical system will be examined using measures of salivary cortisol. Observational techniques will be used to score behavioral state, coping strategies, and sensitivity/responsivity of caregiving. Collaborative efforts with other laboratories will be used to examine the linkages between adrenocortical activity and other stress-relevant systems as listed above. The proposed studies will provide basic data in the areas of psychobiology as such information pertains to child development and pediatric behavioral medicine. The long-term goals are to gain a better understanding of stress and coping in human infants.